Controllable Synthesis And Performance Of Novel Two-dimensional Materials And Heterostructures

Atomically thick two-dimensional?2D?materials have become the most promising candidates for the next generation of multifunctional electronic information materials,due to their regulable band structure,high carrier mobility and excellent photoelectronic performance.More and more 2D materials have been exploited and preparaed,especially graphene and VIB transition metal dichalcogenides?TMDs?such as MoS₂.However,researches on some novel 2D materials with excellent properties,such as IVB TMDs and non-layered materials are sluggish.Large-area ultrathin samples with high quality are hard to synthesize due to the strong coupling forces,which seriously restrict the development and application of multifunctional devices.Therefore,it is urgent to search an effective synthetic method.Chemical vapor deposition?CVD?is the one of the synthesis methods to prepare high-quality 2D materials controllably,which has advantages of low cost and wide application range.However,there are many challenges faced by CVD:1.Because materials with strong interlayer coupling forces exists in three-dimensional form,how to restrain the thermodynamic growth and restrict the longitudinal growth of the material is the research difficulty to synthesize ultrathin and monolayer materials;2.How to avoid uncontrolled and redundant nucleation centers is the key to prepare large-area and two-dimensional materials;3.Due to the lattice mismatch and different binding energy,the growth rate of each lattice plane is different,it is hard to achieve the controllable synthesis of materials'layers,morphology and orientation.In consideration,a simple space-confined CVD was proposed to synthesis high-quality novel 2D materials and heterostructures controllably,and the influence of the confined space on the growth dynamics of materials is discussed.The main research contents in this paper are as follows:1.Comparing with traditional CVD synthesis system,space-confined CVD method provides a stable airflow environment for the growth of 2D materials and protects substrates and sample from the pollution of impurities by introducing a confined space.With introducing confined space,the growth of materials is controlled by dynamics instead of thermodynamics.The precursor concentration is critical for controllable growth of 2D materials by reaserching the relationship of confined space,the distribution of gas velocity and precursor concentration.It can be adjusted by confined space to realize materials'controllable growth.On the one hand,low nucleation density can be obtained for samples with large size.On the other hand,the growth of materials will rely on the diffusion process instead of the reaction process with the changing of precursor concentration,resulting in the controllable synthesis of monolayer to few-layer samples.2.Novel layered HfS₂ nanosheets are synthesized by space-confined CVD.Hexagonal HfS₂ nanosheets with a thickness of 1.2 nm and the size of 5?m were obtained by adjusting the characteristic size of confined space.The morphology of HfS₂ nanosheets can transform from the triangle,circular,hexagon to truncated triangle.The HfS₂nanosheet gained is an n-type semiconductor with a band gap of about 2.0 eV.The photodetector based on the HfS₂ nanosheet appears great performance with a fast response time?⁵5 ms?and a high responsivity(R_?².78 mA W^-1)in visible light range.3.It is difficult to obtain the atomically thick nanosheets of non-layered materials due to atoms are coupled by chemical bonds.In this paper,a small space is constructed by"face to face"stacking two micas,which contributes to restrict the growth of non-layered materials along the vertical direction of substrates.The regulation of confined space to precursor concentration and growth dymanics process was studied,and triangular?-In₂S₃ nanosheets with a thickness of about 1 nm and a large size around 40?m were synthesized.In₂S₃ shows a broad photoluminescence peak ranging from 700 nm to 900nm for the intrinsic defects,which has a good application prospect in wide-spectrum photodetection and near-infrared detection.Moreover,a graphene/In₂S₃ heterojunction was built via mechanical transfer method and the migratory direction of photo-generated carriers in the heterojunction region was discussed.The photodetector based on the heterojunction shows a good performance(?=532 nm,R_??257.7 mA W^-1).4.Expand the space-confaced CVD method for the preparation of complex heterostructures:?1?in-situ construct the heterostructure of In₂S₃/ReS₂/CFP nanosheets by growing In₂S₃ on ReS₂/CFP.The novel heterostructure was applied for photoelectrochemistry and showed a much better performance than ReS₂/CFP;?2?the mulberry-shaped NiS/Ni heterostructure supported by carbon cloth was prepared and used in the field of catalysis,showing an excellent catalytic activity.